Session Manager is an essential add-on for Firefox that saves multiple website as a group and restore them all when you want to visit those website. Firefox Session Manager works as a single bookmark that stores multiple website URLs in it.

Firefox Session Manager :

If you are working with multiple tabs and need to save these website because you want to take a break and work with them later or your Firefox need a restart, you can use Firefox Session Manager to save all the current open website as a session and reopen that session later. Firefox Session Manager has a auto session saving option that will save your current Firefox session in a given time interval automatically. Firefox Session Manager saves your session as a file, so you can make your session parable.